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· Registered
949 Posts
Guess we could just push the little blue button and ask OnStar, they know everything...:D

· Premium Member
552 Posts
Pressure gauges are still best... Dial gauges are even easier to read

Interestingly enough, it is possible to detect low tire pressure in one of the tires using the built-in sensors on an ABS equipped car. Basically, there is a wheel rotation sensor, and if the counts for rotations of one wheel are high relative to the average of the others, it's a good bet that tire's low.

There are some GM vehicles which will produce this as an error code through the OBD2 port.... I don't know if it will come up on the DIC [Driver Information Center] though.

Really, the best way to monitor your tire pressure is a gauge. The one that I use for my tires both every day and out at the track is the Truflate:

This gauge has a very low volume, so you don't wind up draining much air out of the tire when you sample the pressure.

You press it onto the valve stem, and release. Then, you can bring the gauge up close enough to read, just holding it in your hand--the gauge housing holds the pressure to allow easy reading. The button on the shaft releases the valve, holding the pressure in the chamber, and you're ready to move on to the next tire.

Keeping your tires up to the recommended pressure can dramatically improve fuel mileage. Conversely, running the tires low will cause premature ware of the tire, poor gas mileage, and lowered grip in cornering situations.

Also, even a difference of 2 or 3 pounds between tires on the left versus tires on the right may cause the car to "pull" to one side or the other.

The little lights are nice, but I prefer being able to see the pressure and know that I'm within 1 pound per square inch [PSI] in my left to right balance.

Also note, that there is a reason that the Manufacturers usually have the rear tires at a slightly lower pressure than the front tires. It has to do with total weight loading, and also more importantly, stability and grip characteristics. It comes down to this, if you run the rear tires too high, you can have more dramatic transient grip characteristic changes for the rear tires, and the car may be more likely to spin. This was particularly true of the rear engine Corvair, and the manufacturer had a surprisingly lower inflation recomendation for the rear tires than we see on most cars today.

To really get the tire pressures correct, you use a pyrometer to measure the temperature of the tire at three spots on the tire after a run on the track. If you have fairly even temperatures across the three spots (outside edge, middle, and inside edge) then you're getting consistent and fairly close to optimum tire performance. Here's a picture of the one that I use:

If the center is hotter, then the pressure is too high. If the outside and inside are both hotter, then the pressure is too low.

Sometimes, you'll see the too low pressure condition come in with a higher outer edge temperature, cooler middle and a colder inner edge temperature. In that case, try raising the pressure a bit (3-4 pounds) and see if the center and inner edge warm up a bit. I've found that a pressure change of as little as 2 pounds is enough to make a 5-10 degree difference in the temperature distribution.

Another tell tale sign that your tire pressure is too low is if you see scrub marks on the sidewall of the tire after a particularly aggressive turn with a lot of lateral cornering force being generated. This is a good indication that the tire pressure is too low, and the tire is distorting and allowing the sidewall to touch the pavement during high force cornering.

I record my tire pressures, and after several track days, I'm getting fairly consistent temps across the entire face of the tire. You'll always have a bit higher temperature on the outer edge than the inner edge, but you can get reasonably close.

Tire pressure can also tell you if you've got an alignment problem. If the inside edge is hotter than the outside edge, you've got too much camber dialed in.... However, reading tire temperatures for alignment settings is a bit beyond the scope here, and straying a bit far afield.

Here's the deal:
  • Check your tire pressure about every other time you fill up. If it looks soft and squashed down, it probably is about 5 to 10 lbs too low.
  • Start with the manufacturer's recommended tire pressure, but never exceed the maximum pressure imprinted on the side wall of the tire.
  • If you see signs of unusual wear, take it to the shop and discuss it with a mechanic or tire professional. Training and experience varies, but if you learn a little about your own tires first, you'll understand better what they are saying (and sometimes be able to spot folks who might need a bit more training or experience... ;))

· Registered
1,707 Posts
tire gauges

Do not get the little tire caps, the ones w/ red/green indicators- I used them on my Tahoe, bad readings; also see if you can find a tire dealer in your area that has nitrogen to fill the tires; all the pro teams use N2, it doesn't change pressure with temp like air.

· Premium Member
2,130 Posts
Robotech said:
Isn't a tire pressure monitoring system part of our DIC?

Never looked into I'm Grand Prix has it but I don't remember anything on the Sky about it. If not, I like those little gadgets.
Nope, no pressure monitor. Since the car doesn't have run flats it's not required.
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